Conversions are understood to mean the engines of another area that have been adapted for their aeronautical use, especially those of cars and motorcycles.

-Maybe the first ones were in amateur construction, homebuilts and experimental: it is known that Harley-Davidson and Indian motorcycle engines were used, as well as Henderson. And regarding cars, the oldest may have been the Ford Model A, since its appearance, and until today some still fly.

-In the 1950's the German Volkswagen car engine began to be used and until today it is still flying. All models and displacements have been used, even two cylinders have been removed from the original engine, like the Half-Volkswagen.

-Lately, Subaru engines are being converted, also with horizontally opposed cylinders to the point of -nearly- putting aside Volkswagen.

-Also big American car engines like Ford and especially those of GM (Chevrolet mainly) have taken a power zone in a very exclusive way.

-To illustrate we list some current brands with the type of engines that they modify and convert, generally applying PSRU (Reduction), specially built for many models of engines.

-Aero Conversions, uses Volkswagen.
-Aero Momentum,  Suzuki G series
-Airdrone Aeroplanes, Volkswagen.
-Air Trikes, los Geo/Suzuki, Honda, BMW, Subaru.
-Atkins Rotary, Wankel rotaries.
-Auto PSRU, GM and Subaru gears (Former Geared
Drives)
-Auto Flight, Subaru EA, EJ series and others.
-D-Motor, FireWallForward of new design.
-EPI Inc, GM, Ford, Jaguar (V12 EPI).
-Firewall Forward, Honda VTEC and GMs
-Fly Corvair, Chevrolet Corvair
-Fly Eco, Mercedes Benz
-Great Plains A/C Supply, Volkswagen
-Haas Power Air, Ford
-Hexadyne Aviation, new axial design
-Hummel Engines, Volkswagen
-Mistral engines, Mazda RX-7
-Pegasus, Half Continental O-200
-RAM Performance, Subaru
-Raven Re-Drives, Suzuki, Geo, Honda
-Revmaster Aviation, Volkswagen
-Prop Drives Inc, Rotary (Wankels), Subaru and others
-Robinson V-8 Power A/C, General Motors
-Stratos 2000, Subaru
-Take-Off GmBH, BMW
-Titqan A/C, Subaru y Honda
-Valley Engineering, V-Twin VW
-Viking A/C Engine, Honda Fit
-Volks Wagen engine Center, VW